Income, or even 6mo income history, doesn't predict how likely you'll be to get another job if you lose your job. What lenders really want to know is how in-demand you are in the market, and so what they should predict as the "floor" on your future income.

Add to that how likely someone with your personality-type is to just decide to take a few months/years off between jobs living off of savings, and you've got a heuristic nearly as predictive of loan-repayment as all the rest of the information lenders use today put together.